URLConnection is not allowing me to access data on Http errors (404,500,etc)

Question

I am making a crawler, and need to get the data from the stream regardless if it is a 200 or not. CURL is doing it, as well as any standard browser.

The following will not actually get the content of the request, even though there is some, an exception is thrown with the http error status code. I want the output regardless, is there a way? I prefer to use this library as it will actually do persistent connections, which is perfect for the type of crawling I am doing.

package test;

import java.net.*;
import java.io.*;

public class Test {

    public static void main(String[] args) {

         try {

            URL url = new URL("http://github.com/XXXXXXXXXXXXXX");
            URLConnection connection = url.openConnection();

            DataInputStream inStream = new DataInputStream(connection.getInputStream());
            String inputLine;

            while ((inputLine = inStream.readLine()) != null) {
                System.out.println(inputLine);
            }
            inStream.close();
        } catch (MalformedURLException me) {
            System.err.println("MalformedURLException: " + me);
        } catch (IOException ioe) {
            System.err.println("IOException: " + ioe);
        }
    }
}

Worked, thanks: Here is what I came up with - just as a rough proof of concept:

import java.net.*;
import java.io.*;

public class Test {

    public static void main(String[] args) {
//InputStream error = ((HttpURLConnection) connection).getErrorStream();

        URL url = null;
        URLConnection connection = null;
        String inputLine = "";

        try {

            url = new URL("http://verelo.com/asdfrwdfgdg");
            connection = url.openConnection();

            DataInputStream inStream = new DataInputStream(connection.getInputStream());

            while ((inputLine = inStream.readLine()) != null) {
                System.out.println(inputLine);
            }
            inStream.close();
        } catch (MalformedURLException me) {
            System.err.println("MalformedURLException: " + me);
        } catch (IOException ioe) {
            System.err.println("IOException: " + ioe);

            InputStream error = ((HttpURLConnection) connection).getErrorStream();

            try {
                int data = error.read();
                while (data != -1) {
                    //do something with data...
                    //System.out.println(data);
                    inputLine = inputLine + (char)data;
                    data = error.read();
                    //inputLine = inputLine + (char)data;
                }
                error.close();
            } catch (Exception ex) {
                try {
                    if (error != null) {
                        error.close();
                    }
                } catch (Exception e) {

                }
            }
        }

        System.out.println(inputLine);
    }
}

Answer 1

Simple:

URLConnection connection = url.openConnection();
InputStream is = connection.getInputStream();
if (connection instanceof HttpURLConnection) {
   HttpURLConnection httpConn = (HttpURLConnection) connection;
   int statusCode = httpConn.getResponseCode();
   if (statusCode != 200 /* or statusCode >= 200 && statusCode < 300 */) {
     is = httpConn.getErrorStream();
   }
}

You can refer to Javadoc for explanation. The best way I would handle this is as follows:

URLConnection connection = url.openConnection();
InputStream is = null;
try {
    is = connection.getInputStream();
} catch (IOException ioe) {
    if (connection instanceof HttpURLConnection) {
        HttpURLConnection httpConn = (HttpURLConnection) connection;
        int statusCode = httpConn.getResponseCode();
        if (statusCode != 200) {
            is = httpConn.getErrorStream();
        }
    }
}